1. Field of the Invention
The present invention relates to an adaptive torque model for use in controlling a multi-cylinder internal combustion engine.
2. Background Art
Torque-based engine control strategies use various engine actuators, such as airflow or throttle, fuel, spark, etc. to produce an engine torque consistent with a desired engine torque based on driver demand and current operating conditions. Closed-loop control requires feedback of the actual engine torque which is compared to the desired torque with the controller acting to reduce the error between the actual and desired torque. While a torque sensor may be used to provide the feedback signal, many applications do not use a torque sensor for a variety of reasons. In these applications, a torque model predicts or estimates the engine torque produced based on engine operating variables. The estimated engine torque is used as feedback to provide a xe2x80x9cpseudoxe2x80x9d closed-loop control, although the strategy is technically an open-loop control because the actual torque produced is not being measured. The torque model may be based on both analytical and empirical data for typical performance of a nominal engine.
With normal manufacturing variations and engine aging, the torque model may be less accurate and result in torque delivery errors. Unlike conventional control strategies where the driver could easily compensate for torque delivery errors by adjusting accelerator pedal position, more advanced control strategies may rely on an accurate engine torque determination to reduce emissions, improve fuel economy and/or improve driveability. For example, in direct injection spark ignition (DISI) engines, including direct injection stratified charge (DISC) engines, an inaccurate torque model may result in noticeable disturbances when engine operating variables change during combustion mode transitions.
An object of the present invention is to provide a system and method for controlling an internal combustion engine using an open-loop control strategy based on an adaptive model to estimate or predict a first engine variable with one or more model parameters adjusted using a second engine operating variable which is measured.
In carrying out the above object and other objects, features, and advantages of the present invention, a method for controlling a multi-cylinder internal combustion engine includes determining a first engine operating variable using a model having at least one adjustable model parameter, measuring a second engine operating variable, and modifying the at least one adjustable model parameter based on a relationship between the first and second engine operating variables. In one embodiment, the first engine operating variable refers to engine torque while the second engine operating variable is engine speed. An engine torque model and/or load torque model may be used to determine an estimated engine speed trajectory which is compared to the actual engine speed trajectory determined using an engine speed sensor. One or more model parameters for the engine torque and/or load torque model are adjusted when appropriate operating conditions are met based on a difference between the predicted or estimated engine speed trajectory and the measured engine speed trajectory. The engine is controlled using the adjusted torque model.
The present invention provides a number of advantages. For example, the adaptive model-based control strategy according to the present invention is capable of compensating for variation in engine operation, such as due to engine aging or manufacturing tolerances. An adaptive model used to estimate or predict one or more engine variables provides a more robust control strategy while reducing the number of necessary sensors. More accurate and consistent variable estimation may also improve driveability, particularly during combustion mode transitions which occur in more advanced engine control strategies.
The above advantages and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.